feat(parser): improve diagnostic messages for merge conflicts

[camc314]

Adds detection and improved error messages for version control merge conflicts encountered in the parser.

This is based upon rustc's implementation.

[camc314]

• feat(parser): improve diagnostic messages for merge conflicts #15443 👈 (View in Graphite)
• main

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[Copilot]

Pull Request Overview

This PR adds Git merge conflict marker detection to the parser, providing enhanced error messages when conflict markers (<<<<<<<, =======, >>>>>>>, |||||||) are encountered instead of generic "Unexpected token" errors.

• Implements merge conflict marker detection in the parser with support for diff3 format
• Adds comprehensive error messages with context-aware help text
• Includes test coverage for both valid code with markers in strings/comments and actual conflict markers

Reviewed Changes

Copilot reviewed 2 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
crates/oxc_parser/src/error_handler.rs	Implements is_merge_conflict_marker() and find_merge_conflict_markers() methods for detecting all Git conflict marker patterns
crates/oxc_parser/src/diagnostics.rs	Adds merge_conflict_marker() diagnostic function with detailed help messages for different conflict scenarios
tasks/coverage/misc/pass/diff-markers-in-strings.js	Tests that markers in strings, templates, and comments don't trigger false positives
tasks/coverage/misc/fail/diff-markers.js	Tests actual conflict marker detection in various contexts
tasks/coverage/snapshots/*.snap	Updates test coverage metrics and adds expected diagnostic output for conflict markers

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[codspeed-hq]

CodSpeed Performance Report

Merging #15443 will not alter performance

_{Comparing c/11-04-feat_parser_improve_diagnostic_messages_for_merge_conflicts (da6cf0f) with main (0fa484d)¹}

Summary

✅ 37 untouched

Footnotes

1. No successful run was found on main (5fa6bb8) during the generation of this report, so 0fa484d was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[Boshen]

Merge activity

• Nov 8, 6:51 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Nov 8, 6:51 AM UTC: Boshen added this pull request to the Graphite merge queue.
• Nov 8, 6:59 AM UTC: Merged by the Graphite merge queue.